This invention relates to stacked die semiconductor packages and stacked semiconductor package modules.
A conventional chip package consists of a semiconductor die affixed to a surface of a substrate and electrically interconnected to bonding pads on the substrate surface. The opposite surface of the substrate has an array of solder balls for electrical connection to, for example, a motherboard. The substrate includes, among other things, routing circuitry for mediating appropriate connection between the die and the motherboard. The die and associated interconnection parts are encapsulated with a protective molding.
The die may be affixed with its “active surface” upward, and is then conventionally interconnected by so-called “wire bonding”, in which conductive wires are connected from points on the active surface of the die to the bond pads on the die attach (“upper”) surface of the substrate.
To increase the capacity and performance of the package, a die may be stacked upon a die, to make a stacked die package. A portion of the active surface of the lower die (typically, for example, a peripheral marginal area) is occupied by the wire bonds (the “wire span” area), and no solid piece can be placed directly upon the wire span area. An upper die that is small enough may be placed directly upon another area of the active surface of the lower die (typically, for example, a central region). However, where an upper die is too large to fit within the available region of the lower die, a small sufficiently thick solid spacer (such as a chip of silicon or glass) may be placed directly on the available region of the lower die, and the upper die is then stacked upon the spacer, as shown in FIG. 1A. Part of the upper die overhangs, and this part may crack or break (destroying the electronics in the die), as shown in FIG. 1B, when the overhanging part is loaded (as, for example, during the wire bond process, when the capillary contacts the die). Or, where the die is very thin and the overhang is extensive, the overhanging portion may not crack or break, but may flex excessively during the wire bonding procedure, resulting in unacceptable bonds at the die pads.
Alternatively, to increase capacity and performance, a second package may be stacked upon a die (or upon a lower package) to make a stacked package module. Where a spacer is required, or where the second package is spaced asymmetrically over the die or lower package or over the spacer, part of the upper package overhangs. The overhanging part of the upper package may crack or break or, as may be more likely, the upper package may “tilt” when the overhanging part is loaded.
One way to prevent such breakage or tilt is to provide a support for the overhanging part of the upper die or package.
A conventional way to support the overhang is to provide solid insulating spacers upon the lower substrate, peripheral to the lower die. Another conventional way to support the overhang is to provide solid insulating spacers upon the lower die, within the available region of the active side of the die.